Hemicyanine dyes and optical recording media using the same

ABSTRACT

A hemicyanine dye having formula (1) and an optical recording medium using the hemicyanine dye as an optical recording medium are provided:  
                 
 
     wherein Z is a benzene ring, naphthalene ring or anthracene ring; X 1  is S, O, Se, NR or C(CH 3 ) 2 ; X 2  is S, NR or O, where R is hydrogen or an alkyl group of 1 to 5 carbon atoms; R 1  is hydrogen, halogen atoms, an alkyl group of 1 to 3 carbon atoms or a nitro group; each of R 2  and R 5  is an alkyl group of 1 to 5 carbon atoms; each of R 3  and R 4  is hydrogen, an hydroxy group, an alkyl group of 1 to 4 carbon atoms, halogen atoms or a halide; Y is Cl, Br, I, ClO 4 , BF 4 , BrO 4 , PF 6 , CH 3 SO 3 , CF 3 SO 3 , 4-CH 3 C 6 H 4 SO 3 , C 6 H 5 SO 3 , 6-SO 3 C 10 H 6 SO 3  or HSO 4 ; n is an integer of 0-2; and m is an integer of 1-2. The hemicyanine dye having formula (1) above is easy to synthesize with high yield. Thus, use of the hemicyanind dye as an optical recording medium is advantageous in terms of the manufacturing costs. An optical recording medium using the hemicyanine dye has improved recording characteristics in terms of jitter and modulation factor.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to hemicyanine dyes and opticalrecording media formed using a hemicyanine dye as an optical recordingmaterial, and more particularly, to hemicyanine dyes, and a write onlyread many (WORM) optical recording medium capable of recording andreproducing information by laser, which employs a hemicyanine dye as anoptical recording material.

[0003] 2. Description of the Related Art

[0004] Optical recording media have a smaller recording area perrecording unit than conventional magnetic recording media, so that useof optical recording media as a high density recording medium isextensively increasing. Optical recording media are classified into aread only memory (ROM) type for only reading recorded information, awrite once read many (WORM) type which allows only one writing, and anerasable type which allows erasing of recorded information andrewriting.

[0005] Recordable optical recording media record and reproduceinformation by detecting variations in the reflectivity caused byphysical deformation and changes in phase and magnetic properties of arecording layer before and after the recording.

[0006] A compact disk recordable (CD-R) is widely known as a WORM typeoptical recording medium. In addition, a variety of optical recordingmaterials, which ensure easy manufacture of such a recording medium withimproved properties, have been suggested and some of them are in use.Disclosed optical recording materials for CD-Rs include a cyanine dye(Japanese Patent Publication No. sho 58-125246), a phthalocyanine dye(European Patent No. 676,751), an azo dye (U.S. Pat. No. 5,441,844), adye of double salt (U.S. Pat. No. 4,626,490) and a dye of azo-metalcomplex (U.S. Pat. No. 5,272,047).

[0007] Recently, with increased amount of information, a digitalversatile disk recordable (DVD-R) with increased information storingcapability has been suggested. The DVD-R adopts a red diode laser havinga wavelength of 630-690 nm, as a light source, and has reduced pit sizeand track interval, so that its information storing capacity is 6-8times increased to CD-Rs, with improved recording density. Opticalrecording materials suitable for DVD-Rs needs a high reflectivity andgood absorption at the recording wavelength, and good solubility in anorganic solvent. In addition, the synthesis of optical recordingmaterials must be easy with low costs. Examples of such opticalrecording materials for DVD-Rs include a cyanine dye (Japanese PatentPublication Nos. hei 10-149583 and hei 9-208560) and an azo-metalcomplex (Japanese Patent Publication Nos. hei 10-157293 and hei9-157301). However, it would be desirable to improve the characteristicsof the conventional dyes.

SUMMARY OF THE INVENTION

[0008] To solve the above problems, it is a first objective of thepresent invention to provide a novel hemicyanine dye which is easy tosynthesize with high yield.

[0009] A second objective of the present invention is to provide anoptical recording medium with improved recording characteristics, whichis manufactured using the hemicyanine dye as an inexpensive opticalrecording material.

[0010] The first objective of the present invention is achieved by ahemicyanine dye having formula (1):

[0011] wherein Z is a benzene ring, naphthalene ring or anthracene ring;X, is S, O, Se, NR or C(CH₃)₂; X₂ is S, NR or O, where R is hydrogen oran alkyl group of 1 to 5 carbon atoms; R₁ is hydrogen, halogen atoms, analkyl group of 1 to 3 carbon atoms or a nitro group; each of R₂ and R₅is an alkyl group of 1 to 5 carbon atoms; each of R₃ and R₄ is hydrogen,an hydroxy group, an alkyl group of 1 to 4 carbon atoms, halogen atomsor a halide; Y is Cl, Br, I, ClO₄, BF4, BrO₄, PF₆, CH₃SO₃, CF₃SO₃,4-CH₃C₆H₄SO₃, C₆H₅SO₃, 6-SO₃C₁₀H₆SO₃ or HSO₄; n is an integer of 0-2;and m is an integer of 1-2.

[0012] The second objective of the present invention is achieved by anoptical recording medium comprising a transparent substrate withgrooves, a recording layer including a laser absorptive dye, formed overthe transparent substrate, and a reflective layer and a protective layerformed over the recording layer, wherein the dye of the recording layeris a hemicyanine dye having formula (1):

[0013] wherein Z is a benzene ring, naphthalene ring or anthracene ring;X₁ is S, O, Se, NR or C(CH₃)₂; X₂ is S, NR or O, where R is hydrogen oran alkyl group of 1 to 5 carbon atoms; R₁ is hydrogen, halogen atoms, analkyl group of 1 to 3 carbon atoms or a nitro group; each of R₂ and R₅is an alkyl group of 1 to 5 carbon atoms; each of R₃ and R₄ is hydrogen,an hydroxy group, an alkyl group of 1 to 4 carbon atoms, halogen atomsor a halide; Y is Cl, Br, I, ClO₄, BF₄, BrO₄, PF₆, CH₃SO₃, CF3SO₃,4-CH₃C₆H₄SO₃, C₆H₅SO₃, 6-SO₃C₁₀H₆SO₃ or HSO₄; n is an integer of 0-2;and m is an integer of 1-2.

BRIEF DESCRIPTION OF THE DRAWING

[0014] The above objectives and advantages of the present invention willbecome more apparent by describing in detail a preferred embodimentthereof with reference to the attached drawings in which:

[0015]FIG. 1 is a sectional view illustrating the structure of layersstacked in an optical recording medium according to a preferredembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0016] In a hemicyanine dye having formula (1) according to the presentinvention, Z is a benzene ring, a naphthalene ring or an anthracenering.

[0017] Apparently, in formula (1), the portion (I) including the ringindicated by Z represents a condensed ring formed by covalently couplingat least two atoms between a octagonal ring compound selected from thegroup consisting of thiazole ring, oxazole ring and imidazole ring, andone of the benzene ring, naphthalene ring and anthracene ring. Theconcrete examples of the portion (I) are as follows.

[0018] wherein Z is a benzene ring, naphthalene ring or anthracene ring;X₁ is S, O, Se, NR or C(CH₃)₂; X₂ is S, NR or O, where R is hydrogen oran alkyl group of 1 to 5 carbon atoms; R₁ is hydrogen, halogen atoms, analkyl group of 1 to 3 carbon atoms or a nitro group; each of R₂ and R₅is an alkyl group of 1 to 5 carbon atoms; each of R₃ and R₄ is hydrogen,an hydroxy group, an alkyl group of 1 to 4 carbon atoms, halogen atomsor a halide; Y is Cl, Br, I, C₁₀ ₄, BF₄, BrO₄, PF₆, CH₃SO₃, CF₃SO₃,4-CH₃C₆H₄SO₃, C₆H₅SO₃, 6-SO₃C₁₀H₆SO₃ or HSO₄; n is an integer of 0-2;and m is an integer of 1-2.

[0019] Preferably, the hemicyanine dye having formula (1) is a compoundhaving formula (2) or (3) below:

[0020] wherein R₁ is H, NO₂ or Cl; R₂ is CH₃, C₂H₅, C₃H₇or C₄H₉; X₁ isC(CH₃)₂ or S; X₂ is O or S; R₅ is C₂H₅, C₃H₇ or C₄H₉; and Y is ClO₄,BF₄, PF₆, I, Br or Cl, and

[0021] wherein X₁ is C(CH₃)₂ or S; X₂ is S; R₂ is CH₃, C₂H₅, C₃H₇ orC₄H₉; R₅is C₂H₅, C₃H₇ or C₄H₉; and Y is ClO₄, BF₄, PF₆, I, Br or Cl.

[0022] The synthesis of the novel hemicyanine dye having formula (1)according to the present invention will be described with reference tothe following reaction scheme (I). The hemicyanine dye having formula(1) is obtained by condensing compound (A) with compound (B). Each ofthe compounds (A) and (B) can be derived by the following processillustrated in reaction scheme (I).

[0023] Compound (A) is derived by reacting compound (A-1) with excesshalogen compound, for example, iodomethane, iodoethane, iodopropane,iodobutane. Compound (B) can be derived by reacting compound (B-1) witha secondary amine.

[0024] An optical recording medium according to the present invention,which is manufactured using the hemicyanine dye having formula (1) as anoptical recording material, is a write once read many (WORM) typeoptical recording medium using a laser beam, and particularly, is aDVD-R using a short wavelength laser beam as a light source.

[0025]FIG. 1 is a sectional view illustrating the structure of layersstacked in an optical recording medium according to the presentinvention. Referring to FIG. 1, a recording layer 11, which contains thehemicyanine dye having formula (1) above used as an optical recordingmedium, a reflective layer 12 and a protective layer 13 are deposited insuccession over a semiconductor substrate 10.

[0026] For certain cases, a dummy substrate 15 can be attached to theoptical recording medium using an adhesive layer 14. Alternatively, theoptical recording medium of FIG. 1 can be combined with another opticalrecording medium having the same or different structure as or from thatof FIG. 1. A material used for the adhesive layer 14 may be aultraviolet (UV) curable resin, or a cationic curable resin. Also, suchcombination with an adhesive layer can be performed using a two-sidedadhesive sheet, or by a hot-melting, spin coating, dispensing(extrusion), screen printing, or roll-coat method.

[0027] Preferably, the substrate 10 is formed of a material, which istransparent to a laser beam and easy to swell by heat, and has a strongimpact resistance. Suitable materials for the substrate 10, which meetthe requirements, include polycarbonate, polymethacrylate, epoxy resin,polyester resin and polyolefin resin. These materials used for thesubstrate 10 have a thermal deformation temperature in the range of80-200° C., but preferably in the range of 100-200° C.

[0028] Pregrooves for guiding an incident laser beam during recording orreproducing are formed on the surface of the substrate 10. Preferably,the pregrooves have a depth of 80-250 nm, and a width of 200-500 μm.Preferably, the substrate 10 has a transmittance of 60-99%, with about90% being preferred, and a thickness of 0.01-10 mm. If the transmittanceor thickness of the substrate is beyond the above range, the opticalrecording medium characteristics are unfavorable.

[0029] The recording layer 11 includes an organic dye which isphysically deformed and decomposed by a recording laser beam. In thepresent invention, the recording layer 11 may include at least onehemicyanine dye having formula (1). As needed, the recording layer 11can further include a singlet oxygen quencher, a light absorptivematerial and a radical scavenger. Preferably, the optical recordingmaterial used in the recording layer 11 has a complex refractive index,including a real part coefficient n of 1.5-2.8 and an imaginary partcoefficient k of 0.01-0.4 in the wavelength range for recording andreproduction. More preferably, the optical recording material has arefractive index of 1.8-2.3 in a wavelength range of 400-700 nm.Preferably, the optical recording medium has a maximum absorptionwavelength of 350-650 nm. If the complex refractive index and themaximum absorption wavelength of the optical recording material arebeyond the above ranges, recording and reproducing characteristics interms of recording sensitivity, push-pull, tracking and modulationfactor are unfavorable.

[0030] The recording layer 11 is formed by spin coating a compositionover a substrate. The composition for the recording layer 11 is obtainedby dissolving 0.5-10% by weight hemicyanine dye having formula (1) in asolvent of 90-99.5% by weight based on the total weight of thecomposition. Any solvent capable of dissolving the hemicyanine dye canbe used without limitations.

[0031] Preferably, the reflective layer 12, which ensures highreflectivity for recording or reproducing, is formed of a metal having ahigh reflectivity as well as a high thermal conductivity, such that thereflective layer 12 is not susceptible to deform. Suitable metals usedfor the reflective layer 12 include gold (Au), aluminum (Al), silver(Ag), copper (Cu), palladium (Pd), platinum (Pt), titanium (Ti),tantalum (Ta), chromium (Cr), nickel (Ni) or an alloy of these metals.Preferably, the reflective layer 12 has a thickness of 500-2500 ∪. Thereflective layer 12 may be formed by vacuum deposition, E-beam orsputtering.

[0032] In the present invention, the protective layer 13 serves toprotect other constituents layers, and in particular, the reflectivelayer 12 of the optical recording medium. The protective layer 13 isformed by a common method. For example, a transparent UV curablematerial with strong impact resistance, such as epoxy or acrylate UVcurable resin is spin-coated over the reflective layer 12, and thencured by radiation of UV rays.

[0033] The present invention will be described in greater detail bymeans of the following examples. The following examples are forillustrative purposes and are not intended to limit the scope of theinvention.

SYNTHESIS EXAMPLE 1

[0034] 1 Equivalent 5-bromo-2-thiophenecarboxaldehyde was dissolved indimethylformamide, and 1-2 drops of Aliquart 336(tricaprylylmethylammonium chloride, produced by Aldrich) was dropwiseadded to the solution. 10 Equivalents diethyl amine was added to themixture and refluxed at 110° C. for 5 days.

[0035] The reaction mixture was evaporated in a vacuum to remove thesolvent, and the residue was extracted with ether. The ether portion wasconcentrated and purified by silicagel chromatography (using a mixedsolvent containing hexane and ethylacetate in a ratio of 3:1 by volumeas an eluent) to obtain 5-diethylamino-2-thiophenenecarboxaldehyde oforange color with a yield of 80%.

[0036] 1 Equivalent 2,3,3-trimethylindolene and 10 equivalentsiodomethane were dissolved in ethylacetate, and refluxed at 50° C. As aresult, when excess reaction product was precipitated, the precipitatewas filtered and washed with ethyl acetate several times, so that1-methyl-2,3,3-trimethylpseudoindolium iodide was obtained with a yieldof 90%.

[0037] 1.2 Equivalents 5-diethylamino-2-thiophenecarboxaldehyde and 1equivalent 1-methyl-2,3,3-trimethylpseudoindolium iodide were dissolvedin ethanol while stirring. Then, 1 drop of piperidine was added. Thereaction mixture was refluxed for 5 hours and evaporated under vacuum toremove the solvent. Then, excess ethyl acetate was added to theresultant mixture, so that violet powder was precipitated. Theprecipitate was washed with ethyl acetate several times, so that dye Dlof violet color having the following formula was obtained with a yieldof 80%.

[0038] 0.3g of the dye D1 was dissolved in 10 ml tetrafluoropropanol,and spin-coated over a substrate to form a dye thin film. The absorptionspectrum of the obtained thin film was observed with UV-VIS-NIRspectrophotometer (UV-3101 PC, Shimadzu Co.). As a result, the maximumabsorption peak (Amax) of dye D1 was shown at 590 nm.

[0039] NMR (DMSO, ppm): 1.28 (t, 6H), 1.68 (s, 6H), 3.68 (q, 4H), 3.96(s, 3H), 6.08 (d,1 H), 6.76 (d,1 H), 7.42 (t,1 H), 7.64 (t, IH), 7.82(d, 1H), 7.90 (d, 1H), 8.04 (d, 1H), 8.36 (d, 1H)

SYNTHESIS EXAMPLE 2

[0040] 2-Methylene-1,3,3-trimethyleneindoline was dissolved in ethylacetate and a HCl solution was dropwise added to the solution. Theprecipitate was filtered from the reaction mixture and washed with ethylacetate several times to obtain 1,2,3,3,-tetramethylpseudoindoliumchloride.

[0041] Dye D1 of violet color having the following formula was obtainedwith a yield of 85%) in the same way as in Synthesis Example 1, exceptthat 1,2,3,3,-tetramethylpseudoindolium chloride was used instead of1-methyl-2,3,3-trimethylpseudoindolium iodide of Synthesis Example 1.

[0042] The maximum absorption peak (λ_(max)) of dye D2 was observed bythe same method as in Synthesis Example 1. As a result, Amax of dye D2was shown at 586 nm.

[0043] NMR (DMSO, ppm): 1.28 (t, 6H), 1.68 (s, 6H), 3.68 (q, 4H), 3.96(s, 3H), 6.08 (d, 1H), 6,76 (d, 1H), 7.42 (t, 1H), 7.64 (t, 1H), 7.82(d, 1H), 7.90 (d, 1H), 8.04 (d,1 H), 8.36 (d,1 H)

SYNTHESIS EXAMPLES 3 THROUGH 7

[0044] Dyes D3, D4, D5, D6 and D7 having the following formula wereobtained in the same way as in Synthesis Example 2, except that HCl usedin Synthesis Example 2 was replaced by HBr, H₂SO₄, HClO₄, HBF₄ and HPF₆,respectively, for Synthesis Examples 3 through 7. The yields of dyes D3,D4, D5, D6 and D7 were 70%, 75%, 75%, 70% and 75%, respectively.

[0045] In the formula above, Y is Br for dye D3, ClO₄ for dye D4, HSO₄for dye D5, BF₄ for dye D6, and PF₆ for dye D7.

[0046] The maximum absorption peaks (λ_(max)) of dyes D3, D4, D5, D6 andD7 were observed by the same method as in Synthesis Example 1. As aresult, λ_(max) was 590 nm for dye D3, 586 nm for dye D4, 589 nm for dyeD5, 589 nm for dye D6, and 590 nm for dye D7.

[0047] <Dye D3>

[0048] NMR (DMSO, ppm): 1.28 (t, 6H), 1.68 (s, 6H), 3.68 (q, 4H), 3.96(s, 3H), 6.08 (d, 1H), 6.76 (d,1 H), 7.42 (t, 1H), 7.64 (t,1 H), 7.82(d,1 H), 7.90 (d, 1H), 8.04 (d, 1H), 8.36 (d,1 H)

[0049] <Dye D4>

[0050] NMR (DMSO, ppm): 1.28 (t, 6H), 1.68 (s, 6H), 3.68 (q, 4H), 3.96(s, 3H), 6.08 (d, IH), 6.76 (d,1 H), 7.42 (t, 1H), 7.64 (t,1 H), 7.82(d,1 H), 7.90 (d,1 H), 8.04 (d, 1H), 8.36 (d, 1H)

[0051] <Dye D5>

[0052] NMR (DMSO, ppm): 1.28 (t, 6H), 1.68 (s, 6H), 3.68 (q, 4H), 3.96(s, 3H), 6.08 (d, 1 H), 6.76 (d, 1H), 7.42 (t, 1 H), 7.64 (t, 1H), 7.82(d, 1H), 7.90 (d, 1H), 8.04 (d, I H), 8.36 (d, 1 H) <Dye D6>

[0053] NMR (DMSO, ppm): 1.28 (t, 6H), 1.68 (s, 6H), 3.68 (q, 4H), 3.96(s, 3H), 6.08 (d, I H), 6.76 (d, 1 H), 7.42 (t, 1H), 7.64 (t, 1 H), 7.82(d, 1 H), 7.90 (d, 1H), 8.04 (d, 1H), 8.36 (d, 1H)

[0054] <Dye D7>

[0055] NMR (DMSO, ppm): 1.28 (t, 6H), 1.68 (s, 6H), 3.68 (q, 4H), 3.96(s, 3H), 6.08 (d, 1 H), 6.76 (d, 1 H), 7.42 (t, 1H), 7.64 (t, 1H), 7.82(d, I H), 7.90 (d, 1H), 8.04 (d, 1H), 8.36 (d, 1H)

[0056] SYNTHESIS EXAMPLE 8

[0057] Dye D8 having the following formula was obtained with a yield of75% in the same way as in Synthesis Example 2, except that5-chloro-1,2,3,3,-tetramethylpseudoindolium chloride was used instead of1-methyl-2,3,3-trimethylpseudoindolium iodide of Synthesis Example 1.

[0058] The maximum absorption peak (Amax) of dye D8 was observed by thesame method as in Synthesis Example 1. As a result, λ_(max) was 596 nmfor dye D8.

[0059] NMR (DMSO, ppm): 1.28 (t, 6H), 1.68 (s, 6H), 3.62 (s, 3H), 3.70(q, 4H), 6.02 (d, 1H), 6.82 (d, 1H), 7.40 (d, 1H), 7.46 (d, 1H), 7.74(s, 1H), 8.10 (d, 1H), 8.20 (d, 1 H)

SYNTHESIS EXAMPLES 9 THROUGH 11

[0060] Dyes D9, D10 and D11 having the following formula were obtainedin the same way as in Synthesis Example 2, except that5-chloro-2-methylene-1,3,3-trimethylindoline was used instead of2-methylene-1,3,3-trimethylene indoline, and HCl used in SynthesisExample 2 was replaced by HClO₄, HBF₄ and HPF₆, respectively, forSynthesis Examples 9 through 11. The yields of Dyes D9, D10 and D11 were70%, 75% and 75%, respectively.

[0061] In the formula above, Y is ClO₄ for dye D9, BF₄ for dye D10, andPF₆ for dye D11.

[0062] The maximum absorption peaks (Amax) of dyes D9, D10 and D11 wereobserved by the same method as in Synthesis Example 1. As a result,λ_(max) was 597 nm for dye D9, 599 nm for dye D10 and 598 nm for dyeD11.

[0063] <Dye D9>

[0064] NMR (DMSO, ppm): 1.28 (t, 6H), 1.68 (s, 6H), 3.62 (s, 3H), 3.70(q, 4H), 6.04 (d, 1H), 6.82 (d, 1 H), 7.40 (d, 1H), 7.46 (d, I H), 7.76(s, 1H), 8.06 (d, 1H), 8.36 (d,1 H)

[0065] <Dye D10>

[0066] NMR (DMSO, ppm): 1.28 (t, 6H), 1.68 (s, 6H), 3.62 (s, 3H), 3.70(q, 4H), 6.04 (d, 1H), 6.82 (d, 1H), 7.40 (d, 1H), 7.46 (d, 1H), 7.76(s, 1H), 8.06 (d, 1H), 8.36 (d, 1 H)

[0067] <Dye D11>

[0068] NMR (DMSO, ppm): 1.28 (t, 6H), 1.68 (s, 6H), 3.62 (s, 3H), 3.70(q, 4H), 6.04 (d,1 H), 6.82 (d, 1H), 7.40 (d,1 H), 7.46 (d, 1 H), 7.76(s, 1 H), 8.06 (d, 1H), 8.36 (d, 1H)

SYNTHESIS EXAMPLE 12

[0069] 1 Equivalent 2,3,3,-trimethyl-4,5-benzo-3H-indoline and 10equivalents iodomethane were dissolved in ethyl acetate and refluxes at50° C. When excess reaction product was precipitated, the precipitatewas filtered and washed with ethyl acetate several times to obtain1,2,3,3-tetramethyl-4,5-benzo-pseudindolium iodide.

[0070] Dye D12 of violet color was obtained with a yield of 80% by thesame method as in Synthesis Example 1, except that1-methyl-2,3,3-trimethylpseudoindolium iodide was replaced by1,2,3,3-tetramethyl-4,5-benzopseudoindolium iodide.

[0071] The maximum absorption peak (λ_(max))of dye D12 was observed bythe same method as in Synthesis Example 1. As a result, λ_(max), was 620nm for dye D12.

[0072] NMR (DMSO, ppm): 1.28 (t, 6H), 1.92 (s, 6H), 3.68 (q, 4H), 3.78(s, 3H), 6.12 (d, 1H), 6.72 (d, 1H), 7.52 (t, 1H), 7.66 (t, 1H), 7.74(d, 1H), 8.02 (d, 1H), 8.08 (d, 1H), 8.12 (d, 1H), 8.26 (d, 1H), 8.48(d, 1H)

[0073] SYNTHESIS EXAMPLE 13

[0074] 1,2,3,3-tetramethyl-4,5-benzopseudoindolium iodide obtained inSynthesis Example 12 was dissolved in 2M NaOH solution, and ethylacetate was added to the solution and stirred for 2 minutes. The ethylacetate portion was separated from the reaction mixture and HClO₄solution was added to the separated ethyl acetate portion. Theprecipitate of the reaction mixture was filtered and washed with ethylacetate several times to obtain 1,2,3,3-tetramethyl-4,5-benzopseudoliumperchlorate.

[0075] Dye D13 having the following formula was obtained with a yield of80% in the same way as in Synthesis Example 1, except that1-methyl-2,3,3-trimethylpseudoindolium iodide used in Synthesis Example1 was replaced by 1,2,3,3-tetramethyl-4,5-benzopseudoindoliumperchlorate.

[0076] The maximum absorption peak (λ_(max)) of dye D13 was observed bythe same method as in Synthesis Example 1. As a result, λ_(max) was 618nm for dye D13.

[0077] NMR (DMSO, ppm): 1.28 (t, 6H), 1.92 (s, 6H), 3.68 (q, 4H), 3.78(s, 3H), 6.12 (d, 1H), 6.72 (d, 1H), 7.52 (t, 1H), 7.66 (t, 1H), 7.74(d, 1H), 8.02 (d, 1H), 8.08 (d, 1H), 8.12 (d, 1H), 8.26 (d, 1H), 8.48(d, 1H)

SYNTHESIS EXAMPLE 14

[0078] Dye 14 having the following formula was obtained in the same wayas in Synthesis Example 1, except that 2-methylbenzothiazole andiodoethane were used instead of 2,3,3-trimethylidolenine and iodomethaneused in Synthesis Example 1, respectively. The yield of dye D14 was 80%.

[0079] The maximum absorption peak (λ_(max)) of dye D14 was observed bythe same method as in Synthesis Example 1. As a result, λ_(max) was 558nm for dye D14.

[0080] NMR (DMSO, ppm): 1.28 (t, 6H), 1.34 (t, 3H), 3.60 (q, 4H), 4.56(q, 2H), 6.56 (d, 1H), 6.64 (d, 1H), 7.45 (t, 1H), 6.40 (t, 1H), 7.86(d, 2H), 8.08 (d, 1 H), 8.10 (d,1 H)

SYNTHESIS EXAMPLE 15

[0081] Dye D15 having the following formula, where R is C₃H₇, wasobtained in the same way as in Synthesis Example 1, except thatiodopropane and 2-methylbenzothiazole were used instead of iodomethaneand 2,3,3-trimethylidolenine used in Synthesis Example 1, respectively.The yield of dye D15 was 75%.

[0082] The maximum absorption peak (λ_(max)) of dye D15 was observed bythe same method as in Synthesis Example 1. As a result, λ_(max) was 560nm for dye D15.

[0083] NMR (DMSO, ppm): 1.20 (t, 6H), 1.24 (t, 3H), 1.30 (q, 2H), 3.50(q, 4H), 4.32 (q, 2H), 6.26 (d,1 H), 6.52 (d,1 H), 7.60 (t, 1H), 7.72(t,1 H), 7.92 (d,1 H), 8.02 (d, 1H), 8.18 (d, 1H), 8.30 (d, 1H)

SYNTHESIS EXAMPLES 16 THROUGH 18

[0084] 1 Equivalent 2-methylene-1,3,3-trimethylindoline, and 10equivalents acid mixture, which contained sulfuric acid and nitric acidin a ratio of 2:1 by equivalent, were mixed and stirred for 30 minutes.The reaction product was neutralized by slowly adding saturated NaOHsolution. The precipitate of orange color was filtered from the reactionmixture and dissolved in ethyl acetate. Triethylamine was added to thesolution to obtain a neutral organic substance and then extracted withethyl acetate. Next, 5-nitro-1,2,3,3-tetramethylpseudoindoliumperchlorate, 5-nitro-1,2,3,3-tetramethylpseudoindolium tetrafluoroborateand 5-nitro-1,2,3,3-tetramethylpseudoindolium hexafluorophosphorate werederived from the product with HClO₄ solution, HBF₄ solution and HPF₆solution, respectively. Dyes D16, D17 and D18 having the followingformula were obtained by the same manner as in Synthesis Example 1,except that the derived products were used instead of1-methyl-2,3,3-trimethylpseudoindolium iodide of Synthesis Example 1.The yields of Dyes D16, D17 and D18 were 75%.

[0085] In the formula above, Y is ClO₄ for dye D16, BF₄ for dye D17, andPF₆ for dye D18.

[0086] The maximum absorption peak (λ_(max)) of dye D16 was observed bythe same method as in Synthesis Example 1. As a result, λ_(max) was 608nm for dye D16, 608 nm for dye D17 and 609 nm for dye D18.

[0087] <Dye D16>

[0088] NMR (DMSO, ppm): 1.25 (t, 6H), 1.70 (s, 6H), 3.60 (s, 3H), 3.78(q, 4H), 6.04 (d, 1H), 7.02 (d, 1H), 7.46 (d, 1H), 8.14 (d, 1H), 8.30(d, 1H), 8.40 (d, 1H), 8.48 (s,1 H)

[0089] <Dye D17>

[0090] NMR (DMSO, ppm): 1.25 (t, 6H), 1.70 (s, 6H), 3.60 (s, 3H), 3.78(q, 4H), 6.04 (d, IH), 7.02 (d, 1H), 7.46 (d, 1H), 8.14 (d, 1H), 8.30(d, 1H), 8.40 (d, 1H), 8.48 (s,1 H)

[0091] <Dye D18>

[0092] NMR (DMSO, ppm): 1.25 (t, 6H), 1.70 (s, 6H), 3.60 (s, 3H), 3.78(q, 4H), 6.04 (d, 1H), 7.02 (d, 1H), 7.46 (d, 1H), 8.14 (d, 1H), 8.30(d, 1H), 8.40 (d, 1H), 8.48 (s, 1 H)

SYNTHESIS EXAMPLE 19

[0093] 1 Equivalent 5-bromo-2-thiophenecarboxaldehyde was dissolved indimethylformamide, and 1-2 drops of Aliquart 336(tricaprylylmethylammonium chloride, produced by Aldrich) was dropwiseadded to the solution. 10 Equivalents dipropylamine was added to themixture and refluxed for 7 days. Next, dipropylamine was removed fromthe reaction mixture, and subjected to extraction and columnchlomatography to obtain 5-dipropylamino-2-thiophenenecarboxaldehydewith a yield of 80%.

[0094] 5-dipropylamino-2-thiophenecarboxaldehyde, instead of5-diethylamino-2-thiophenecarboxaldehyde used in Synthesis Example 1,was reacted with 1-methyl-2,3,3-trimethylpseudoindolium iodide, so thatdye Dl 9 of violet powder having the following formula was obtained withan yield of 80%.

[0095] The maximum absorption peak (λ_(max)) of dye D19 was observed bythe same method as in Synthesis Example 1. As a result, λ_(max) was 597nm for dye D19.

[0096] NMR (DMSO, ppm): 0.94 (t, 6H), 1.66 (s, 6H), 1.72 (m, 4H), 3.60(t, 4H), 3.66 (s, 3H), 6.06 (d, 1 H), 6.78 (d, 1 H), 7.26 (t, 1 H), 7.42(s, 1 H), 7.42 (t, 1 H), 7.62 (d, 1 H), 8.02 (d, 1 H), 8.38 (d, 1 H)

SYNTHESIS EXAMPLE 20

[0097] Dye D20 having the following formula, was obtained in the sameway as in Synthesis Example 1, except that dipropylamine and1,2,3,3-trimethylpseudoindolium perchlorate were used instead ofdiethylamine and 1,2,3,3-trimethylpseudoindolium iodide were used,respectively. The yield of dye D20 was 85%.

[0098] The maximum absorption peak (λ_(max)) of dye D20 was observed bythe same method as in Synthesis Example 1. As a result, λ_(max) was 596nm for dye D20.

[0099] NMR (DMSO, ppm): 0.94 (t, 6H), 1.66 (s, 6H), 1.72 (m, 4H), 3.60(t, 4H), 3.66 (s, 3H), 6.06 (d,1 H), 6.78 (d, 1H), 7.26 (t,1 H), 7.42(s,1 H), 7.42 (t, 1H), 7.62 (d, 1 H), 8.02 (d, 1H), 8.38 (d,1 H)

SYNTHESIS EXAMPLE 21

[0100] Dye D21 having the following formula was obtained with a yield of85% in the same way as in Synthesis Example 19, except that5-chloro-1,2,3,3-tetramethylpseudoindolium iodide was used instead of1-methyl-2,3,3-trimethylpseudoindolium iodide.

[0101] The maximum absorption peak (λ_(max)) of dye D21 was observed bythe same method as in Synthesis Example 1. As a result, λ_(max) was 600nm for dye D21.

[0102] NMR (DMSO, ppm): 0.94 (t, 6H), 1.66 (s, 6H), 1.72 (m, 4H), 3.62(s, 3H), 3.62 (t, 4H), 6.04 (d, 1H), 6.84 (d,1 H), 7.40 (d, I H), 7.46(d, 1 H), 7.74 (s,1 H), 8.04 (d, 1H), 8.34 (d, 1 H)

SYNTHESIS EXAMPLES 22 THROUGH 24

[0103] Dyes D22, D23 and D24 having the following formula were obtainedin the same way as in Synthesis Example 2, except that5-chloro-2-methylene-1,3,3-trimethylindoline was used instead of2-methylene-1,3,3-trimethylindoline, and HC1 used in Synthesis Example 2was replaced by HClO₄, HBF₄ and HPF₆, respectively, for SynthesisExamples 22 through 24. The yields of dyes D22, D23 and D24 were 70%,75% and 75%, respectively.

[0104] In the formula above, Y is ClO₄ for dye D22, BF₄ for dye D23, andPF₆ for dye D24.

[0105] The maximum absorption peaks (λ_(max)) of dyes D22, D23 and D24were observed by the same method as in Synthesis Example 1. As a result,λ_(max) was 600 nm for dye D22, 598 nm for dye D23 and 602 nm for dyeD24.

[0106] <Dye D22>

[0107] NMR (DMSO, ppm): 0.94 (t, 6H), 1.66 (s, 6H), 1.74 (m, 4H), 3.60(t, 4H), 3.61 (s, 3H), 6.02 (d, 1 H), 6.84 (d, 1 H), 7.40 (d,1 H), 7.46(d, 1 H), 7.74 (s, 1 H), 8.04 (d, 1H), 8.32 (d, 1H)

[0108] <Dye D23>

[0109] NMR (DMSO, ppm): 0.94 (t, 6H), 1.66 (s, 6H), 1.72 (m, 4H), 3.60(t, 4H), 3.61 (s, 3H), 6.04 (d,1 H), 6.82 (d,1 H), 7.40 (d, 1H), 7.46(d,1 H), 7.74 (s,1 H), 8.04 (d,1 H), 8.32 (d, 1H)

[0110] <Dye D24>

[0111] NMR (DMSO, ppm): 0.94 (t, 6H), 1.66 (s, 6H), 1.72 (n, 4H), 3.60(t, 4H), 3.61 (s, 3H), 6.02 (d, IH), 6.82 (d, 1H), 7.40 (d, 1H), 7.46(d, 1H), 7.74 (s, 1H), 8.02 (d, 1H), 8.34 (d, 1H)

SYNTHESIS EXAMPLES 25 THROUGH 27

[0112] Dyes D25, D26 and D27 having the following formula were obtainedby the same way as in Synthesis Example 19, except that1-methyl-2,3,3-trimethylpseudoindolium iodide was replaced by5-nitro-2-methylene-1,3,3-trimethylindolium perchlorate,5-nitro-2-methylene-1,3,3-trimethylindolium tetrafluoroborate,5-nitro-2-methylene-1,3,3-trimethylindolium hexafluorophosphate forSynthesis Examples 25 through 27, respectively. The yields of dyes D25,D26 and D27 were 70%, 75% and 75%, respectively.

[0113] In the formula, Y is ClO₄ for dye D25, BF₄ for dye D26, and PF₆for dye D27.

[0114] The maximum absorption peaks (λ_(max)) of dyes D25, D26 and D27were observed by the same method as in Synthesis Example 1. As a result,λ_(max) was 608 nm for dye D25, 608 nm for dye D26 and 604 nm for dyeD27.

[0115] <Dye D25>

[0116] NMR (DMSO, ppm): 0.94 (t, 6H), 1.72 (s, 6H), 1.72 (m, 4H), 3.60(s, 3H), 3.68 (t, 4H), 6.06 (d, 1H), 7.06 (d, 1H), 7.46 (d, 1H), 8.12(d, 1H), 8.28 (d, 1H), 8.38 (d, 1H), 8.50 (s, 1H)

[0117] <Dye D26>

[0118] NMR (DMSO, ppm): 0.94 (t, 6H), 1.70 (s, 6H), 1.72 (m, 4H), 3.60(s, 3H), 3.68 (t, 4H), 6.06 (d, 1H), 7.06 (d, 1H), 7.46 (d, 1H), 8.14(d, 1H), 8.28 (d, 1H), 8.38 (d, 1 H), 8.50 (s,1 H)

[0119] <Dye D27>

[0120] NMR (DMSO, ppm): 0.94 (t, 6H), 1.70 (s, 6H), 1.72 (m, 4H), 3.60(s, 3H), 3.68 (t, 4H), 6.06 (d, 1H), 7.06 (d, 1H), 7.46 (d, 1H), 8.14(d, 1H), 8.28 (s, 1H), 8.38 (d, 1 H), 8.48 (s, 1H)

SYNTHESIS EXAMPLE 28

[0121] Dye D28 having the following formula was obtained with a yield75% by the same way as in Synthesis Example 13, except thatdipropylamine was used instead of diethylamine.

[0122] The maximum absorption peak (λ_(max)) of dye D28 was observed bythe same method as in Synthesis Example 1. As a result, λ_(max) was 618nm for dye D28.

[0123] NMR (DMSO, ppm): 0.94 (t, 6H), 1.72 (m, 4H), 1.92 (s, 6H), 3.60(t, 4H), 3.80 (s, 3H), 6.12 (d, 1H), 6.76 (d, 1H), 7.52 (t, 1H), 7.66(t, 1H), 7.76 (d, 1H), 8.02 (d, 1H), 8.08 (d, 1H), 8.10 (d, 1H), 8.26(d, 1H), 8.46 (d, 1H)

SYNTHESIS EXAMPLES 29 and 30

[0124] Dyes D29 and D30 having the following formula were obtained bythe same way as in Synthesis Example 28, except that1,2,3,3-tetramethyl-4,5-benzopseudoindolium perchlorate was replaced by1,2,3,3-tetramethyl-4,5-benzopseudoindolium tetrafluoroborate and1,2,3,3-tetramethyl-4,5-benzopseudoindolium hexafluorophosphate forSynthesis Examples 29 and 30, respectively. The yield of dyes 29 and 30was 80%.

[0125] In the formula, Y is BF₄ for dye 29 and PF₆ for dye 30.

[0126] The maximum absorption peaks (λ_(max)) of dyes D29 and D30 wereobserved by the same method as in Synthesis Example 1. As a result,λ_(max) was 618 nm for dye D29 and 619 nm for dye D30.

[0127] <Dye D29>

[0128] NMR (DMSO, ppm): 0.94 (t, 6H), 1.72 (m, 4H), 1.92 (s, 6H), 3.60(t, 4H), 3.80 (s, 3H), 6.12 (d, 1H), 6.76 (d, 1H), 7.52 (t, 1H), 7.66(t, 1H), 7.76 (d, 1H), 8.02 (d, 1H), 8.08 (d, 1H), 8.10 (d, 1H), 8.26(d, 1H), 8.46 (d, 1H) <Dye D30>

[0129] NMR (DMSO, ppm): 0.94 (t, 6H), 1.72 (m, 4H), 1.92 (s, 6H), 3.60(t, 4H), 3.80 (s, 3H), 6.12 (d, 1H), 6.76 (d, 1H), 7.52 (t, 1H), 7.66(t, 1H), 7.76 (d, 1H), 8.02 (d, 1H), 8.08 (d, 1H), 8.10 (d, 1H), 8.26(d, 1H), 8.46 (d, 1H)

SYNTHESIS EXAMPLE 31

[0130] 5-Bromofuraldehyde was dissolved in dimethylsulfoxide (DMSO) and1-2 drops of Aliquart 336 (tricaprylylmethylammonium chloride, producedby Aldrich Co.) was added to the solution. 10 Equivalents diethylaminewas added to the mixture and refluxed for 4 days. The remainingdiethylamine was removed from the reaction mixture and subjected toextraction and column chromatography to obtain5-diethylamino-2-furaldehyde with a yield of 85%.

[0131] 1.2 Equivalents 5-diethylamino-2-furaldehyde and 1 equivalent5-chloro-1,2,3,3-tetramethylpseudoindolium perchlorate were dissolved inethanol and 1 drop of piperidine was added to the solution whilestirring.

[0132] The reaction mixture was reacted under reflux for 5 hours, thesolvent was removed from the reaction mixture and excess ethylacetatewas added to obtain violet precipitate. The precipitate was washedseveral times, so that dye D31 of violet color, having the followingformula, was obtained with a yield of 90%.

[0133] The maximum absorption peak (λ_(max)) of dye D31 was observed bythe same method as in Synthesis Example 1. As a result, λ_(max) was 594nm for dye D31.

[0134] NMR (DMSO, ppm): 1.28 (t, 6H), 1.64 (s, 6H), 3.50 (s, 3H), 3.74(q, 4H), 6.04 (d, 1H), 6.36 (d, 1 H), 7.28 (d, 1 H), 7.41 (d, 1 H), 7.60(d, 1 H), 7.67 (d, 1 H), 7.90 (s, 1H)

SYNTHESIS EXAMPLES 32 and 33

[0135] Dyes D32 and D33 having the following formula were obtained bythe same way as in Synthesis Example 30, except that 5-chloro-1,2,3,3-tetramethylpseudoindolium perchlorate was replaced by5-chloro-1,2,3,3-tetramethylpseudoindolium tetrafluoroborate and 5-chloro-1,2,3,3-tetramethylpseudoindolium hexafluorophosphate for SynthesisExamples 32 and 33, respectively. The yield of dyes D32 and D33 was 85%.

[0136] In the formula, Y is BF₄ for dye D32 and PF₆ for D33. The maximumabsorption peaks (λ_(max)) of dyes D32 and D33 were observed by the samemethod as in Synthesis Example 1. As a result, λ_(max) was 594 nm fordye D32 and 595 nm for dye D33.

[0137] <Dye D32>

[0138] NMR (DMSO, ppm): 1.28 (t, 6H), 1.64 (s, 6H), 3.50 (s, 3H), 3.74(q, 4H), 6.04 (d, 1H), 6.36 (d,1 H), 7.28 (d,1 H), 7.41 (d,1 H), 7.60(d,1 H), 7.67 (d, 1 H), 7.90 (s, 1 H)

[0139] <Dye D33>

[0140] NMR (DMSO, ppm): 1.28 (t, 6H), 1.64 (s, 6H), 3.50 (s, 3H), 3.74(q, 4H), 6.04 (d, 1H), 6.36 (d,1 H), 7.28 (d,1 H), 7.41 (d, 1 H), 7.60(d,1 H), 7.67 (d, 1 H), 7.90 (s,1 H)

EXAMPLE 1

[0141] 0.30 g of Dye D9 obtained in Synthesis Example 9 and 0.30 gphenylamine series stabilizer (IRG022, Nippon Kayaku Co., Ltd) weredissolved in 10 ml tetrafluropropanol, and stirred at room temperaturefor 5 hours. The mixture was filtered with a Teflon filter (having 0.2μm pore width) and spin-coated over a substrate to form a dye layer. Thesubstrate was a polycarbonate substrate with 0.6 mm thickness havingpregrooves with 145 nm depth, 30 nm width and 800 nm track pitch.

[0142] The substrate having the dye layer was dried in a vacuum oven setat 40° C. for 12 hours. Then, silver (Ag) was deposited over the dyelayer to form a reflective layer with a thickness of 100 nm. An acrylicUV curable resin was spin coated over the reflective layer and thencured by radiation of UV rays to form a protecting layer. The resultantsubstrate was combined with a dummy disk, thereby completing an opticaldisk.

[0143] EXAMPLES 2 THROUGH 5

[0144] Optical disks were manufactured by the same way as in Example 1,except that dyes D13, D16, D22 and D31 were used instead of dye D9 forExamples 2 through 5.

COMPARATIVE EXAMPLES 1 THROUGH 5

[0145] Optical disks were manufactured by the same way as in Example 1,except that cyanine series dyes, NK4321 (Hayashibara BiochemicalLaboratories, INC.), NK4422 (Hayashibara Biochemical Laboratories,INC.), OM78 (Fuji Photo Film Co., LTD), NK4499 (Hayashibara BiochemicalLaboratories, INC) and NK4500 (Hayashibara Biochemical Laboratories,INC.), were used for Comparative Examples 1 through 5, respectively.

[0146] The characteristics the optical disks manufactured in Examples 1through 5 and Comparative Examples 1 through 5 was evaluated by a DVD-Rrecorder (DVDR-S101, Pioneer), a dynamic characteristic evaluator(DDU-1000, Pulstec) equipped with a laser diode (LD, Nichia, Japan)having a peak wavelength of 630 nm or 650 nm, and a DVD player (DVD909,Samsung, Korea). The before-recording characteristic of the opticaldisks was evaluated using the dynamic characteristic evaluator equippedwith 635 nm LD. The results are shown in Table 1. In Table 1, Rgindicates the reflectivity from pregrooves, RI indicates thereflectivity from lands, P-P indicates the push-pull characteristic,Rtop indicates the maximum reflectivity, the jitter indicates variationsof reproduction signals, which is a signal uniformity index, I14/I14Hindicates the modulated amplitude of recorded signals. TABLE 1 JitterExample Rg (%) RI (%) P-P Rtop (%) (%) I14/I14H Example 1 47 51 0.29 567.8 0.72 Example 2 45 48 0.25 51 8.1 0.67 Example 3 47 53 0.33 54 7.90.70 Example 4 51 56 0.23 59 7.5 0.69 Example 5 48 51 0.24 54 8.0 0.66Comparative 64.1 66 0.33 62 13 0.50 Example 1 Comparative 56 59 0.30 5512 0.58 Example 2 Comparative 56 59 0.33 54 9.6 0.62 Example 3Comparative unrecordable Example 4 Comparative unrecordable Example 5

[0147] As shown in Table 1, the recording characteristics, includingjitter, of the optical disks of Examples 1 through 5, which wereevaluated using the DVD-R recorder, are better than those of ComparativeExamples 1. Also, the reproduction characteristics of Examples 1 through5, evaluated with the DVD player, ensures that the optical disks arecompatible with DVD players. Apparently, the optical characteristics ofthe optical disks of Comparative Examples are unsuitable for recording.

[0148] As previously mentioned, the hemicyanine dye having formula (1)above is easy to synthesize with high yield. Thus, use of thehemicyanind dye as an optical recording medium is advantageous in termsof the manufacturing costs. A WORM type optical recording medium usingthe hemicyanine dye has improved recording characteristics in terms ofjitter and modulation factor, compared with a conventional opticalrecording material.

[0149] While this invention has been particularly shown and describedwith reference to preferred embodiments thereof, it will be understoodby those skilled in the art that various changes in form and details maybe made thereto without departing from the spirit and scope of theinvention as defined by the appended claims.

What is claimed is:
 1. A hemicyanine dye having formula (1):

wherein Z is a benzene ring, naphthalene ring or anthracene ring; X, isS, O, Se, NR or C(CH₃)₂; X₂ is S, NR or O, where R is hydrogen or analkyl group of 1 to 5 carbon atoms; R₁ is hydrogen, halogen atoms, analkyl group of 1 to 3 carbon atoms or a nitro group; each of R₂ and R₅is an alkyl group of 1 to 5 carbon atoms; each of R₃ and R₄ is hydrogen,an hydroxy group, an alkyl group of 1 to 4 carbon atoms, halogen atomsor a halide; Y is Cl, Br, I, ClO₄, BF₄, BrO₄, PF₆, CH₃SO₃, CF₃SO₃,4-CH₃C₆H₄SO₃, C₆H₅SO₃, 6-SO₃CH₆SO₃ or HSO₄; n is an integer of 0-2; andm is an integerof 1-2.


2. The hemicyanine dye of claim 1 , wherein the hemicyanine dye havingformula (1) is a compound having formula (2) or (3):

wherein R₁ is H, NO₂ or Cl; R₂ is CH₃, C₂H₅, C₃H₇ or C₄H₉; X₁ is C(CH₃)₂or S; X₂ is O or S; R₅ is C₂H₅, C₃H₇ or C₄H₅; and Y is ClO₄, BF₄, PF₆,I, Br or Cl, and

wherein X₁ is C(CH₃)₂ or S; X₂ is S; R₂ is CH₃, C₂H₅, C₃H₇ or C₄H₉; R₅is C₂H₅, C₃H₇ or C₄H₉; and Y is ClO₄, BF₄, PF₆, I, Br or Cl.
 3. Anoptical recording medium comprising a transparent substrate withgrooves, a recording layer including a laser absorptive dye, formed overthe transparent substrate, and a reflective layer and a protective layerformed over the recording layer, wherein the dye of the recording layeris a hemicyanine dye having formula (1):

wherein Z is a benzene ring, naphthalene ring or anthracene ring; X₁ isS, O, Se, NR or C(CH₃)₂; X₂ is S, NR or O, where R is hydrogen or analkyl group of 1 to 5 carbon atoms; R₁ is hydrogen, halogen atoms, analkyl group of 1 to 3 carbon atoms or a nitro group; each of R₂ and R₅is an alkyl group of 1 to 5 carbon atoms; each of R₃ and R₄ is hydrogen,an hydroxy group, an alkyl group of 1 to 4 carbon atoms, halogen atomsor a halide; Y is Cl, Br, I, ClO₄, BF₄, BrO₄, PF₆, CH₃SO₃, CF₃SO₃,4-CH₃C₆H₄SO₃, C₆H₅SO₃, 6-SO₃C₁₀H₆SO₃ or HSO₄; n is an integer of 0-2;and m is an integer of 1-2.
 4. The optical recording medium of claim 3 ,wherein the hemicyanine dye having formula (1) is a compound havingformula (2) or (3):

wherein R₁ is H, NO₂ or Cl; R₂ is CH₃, C₂H₅, C₃H₇ or C₄H₉; X₁ is C(CH₃)₂or S; X₂ is O

or S; R₅ is C₂H₅, C₃H₇ or C₄H₉; and Y is ClO₄, BF₄, PF₆, I, Br or Cl,and wherein X, is C(CH₃)₂ or S; X₂ is S; R₂ is CH₃, C₂H₅, C₃H₇ or C₄H₉;R₅ is C₂H₅, C₃H₇ or C₄H₉; and Y is ClO₄, BF₄, PF₆, I, Br or Cl.
 5. Theoptical recording medium of claim 3 , wherein the hemicyanine dye havingformula (1) shows a maximum absorption in the wavelength range of350-650 nm, and has a reflective index of 1.8-2.3 in the wavelengthrange of 400-700 nm.
 6. The optical recording medium of claim 3 ,wherein the substrate has a transmittance of 70-99%, and a thickness of0.01-10 mm.